1. Field of the Invention
The present invention relates generally to distributed power supply circuits, and more particularly to a distributed power supply circuit that supplies common power to multiple packages in an apparatus so that the primary voltage of the common power is converted into a secondary voltage by a voltage converter and supplied to circuits in each package.
2. Description of the Related Art
For example, a transmitter contains multiple packages in a shelf. The shelf supplies common power of, for example, −48 V to each package, and the supplied power is converted into power of, for example, 3.3 V in the power supply circuit of the package and the power of 3.3 V is supplied to each circuit part inside the package. That is, since the packages have their respective power supply circuits, this is referred to as distributed power supply.
Conventionally, the distributed power supply circuit is provided with a monitoring circuit that monitors a primary voltage status. Further, in the case of configuring an apparatus, the distributed power supply circuit is provided with a surge protection circuit, an inrush current prevention circuit, an EMI noise filter, and an input parasitic inductance oscillation prevention circuit on the primary side, and with an insulating OBP (Onboard Power Supply) for conversion into a secondary voltage, an OBP output noise filter, a secondary residual charge discharge circuit, and various loads in accordance with the form of use of a user.
FIGS. 1 and 2 are a block diagram and a circuit diagram, respectively, of a conventional distributed power supply circuit. Referring to FIGS. 1 and 2, diodes and a fuse are provided at a power supply terminal 10 on the negative side (−48 V). A surge protection circuit 11 performs protection against surges using, for example, a varistor that conducts in response to a surge such as lightning or kickback. A power supply monitoring and inrush current prevention circuit 12 prevents an inrush current at the time of turn-on, and monitors the status of a primary voltage. An EMI noise filter 13 removes electromagnetic wave noise. An input parasitic inductance oscillation prevention circuit 14 prevents oscillation due to input parasitic inductance.
Each of insulating OBPs 15 converts a primary power supply of −48 V into a secondary power supply of 3.3 V using, for example, a switching regulator. Each of OBP output noise filters 16 removes noise generated in the corresponding insulating OBP 15. Each of secondary residual charge discharge circuits 17 releases a residual charge on the secondary side.
Japanese Laid-Open Patent Application No. 2005-276034 discloses providing a primary power supply monitoring part and discharging a residual charge by providing a switch for connecting to a resistor for discharging the residual charge on the secondary side of an OBP. Further, Japanese Laid-Open Patent Application No. 9-62408 discloses connecting a diode to the ground-side power supply input of a DC-DC converter and separating an input power supply by the diode.
In the distributed power supply, however, the primary power supply (−48 V) enters a package.
In this case, there is a problem in that a response time necessary for monitoring the primary voltage differs between individual packages, and there is a problem in that at the time of re-inserting a removed package, the packages already installed in the shelf wrongly detect a primary power supply transient.
FIG. 3 is a diagram showing an equivalent circuit at the time of occurrence of abnormality in the power supply. In FIG. 3, the discharge route at the time of occurrence of an output variation such as a voltage drop (a voltage increase from −48 V) in the primary power supply is indicated by arrow. When an instantaneous break occurs in the primary power supply, discharging of an internal capacitor Cin is started. Since there is a reverse connection prevention diode D, the discharge route is closed inside the package so as to pass through an internal resistor Ro of the insulating OBP 15. The internal resistor Ro of the insulating OBP 15 has quite a large value, so that it takes time to discharge the internal capacitor Cin.
The response time, which is a time required for the power supply monitoring and inrush current prevention circuit 12 to determine that the primary voltage is below a predetermined value is determined by the relationship between (a) the total capacitance of capacitors C1 through C7 of the EMI noise filter 13 and the input parasitic inductance oscillation prevention circuit 14 and the total capacitance of secondary-side capacitors on the secondary side (right side) of the insulating OBP 15 and (b) current consumption on the secondary side.
The relationship between the total capacitance of the primary-side and secondary-side capacitors and current consumption on the secondary side differs between multiple packages in a shelf of a transmitter. Therefore, in one package, the response time at the time of a power supply instantaneous break is short so that the package immediately operates, while in another package, the response time is long so that the package is slow to respond. Thus, there is a problem in that the response time required for monitoring the primary voltage differs between individual packages.
Further, at the time of turning off the primary power supply or removing a package, electric charges remain in the capacitors C1 through C7 of the EMI noise filter 13 and the input parasitic inductance oscillation prevention circuit 14. A discharge from these capacitors C1 through C7 causes noise at the time of turning on the primary power supply or inserting a package so as to give impetus to causing variations in the primary supply voltages of other packages in the same shelf. In the worst case, the other packages in the same shelf sharing the primary power supply detect the noise and have a power supply reset, so that a system that should continue operating is temporarily initialized. This causes a problem in that an instantaneous break occurs in an operating line in the transmitter, for example.
In the disclosure of Japanese Laid-Open Patent Applications No. 2005-276034 and 9-62408 described above, the response time at the time of a power supply instantaneous break in power supply monitoring also differs between packages, so that there is the same problem in that electric charges remain in internal capacitors at the time of turning off a primary power supply or removing a package so that noise is generated by a discharge from the capacitors at the time of turning on the primary power supply or inserting a package.